This invention relates to mechanical power transmission systems and more particularly, it concerns a torque transmission system and method by which the torque path between system input and system output is split between at least two infinitely variable transmission units in a manner to optimize the efficiency of each such unit over a wide range of system torque loads and speeds ratios.
Mechanical power transmissions which transmit torque from an input to an output at infinitely variable speed ratios are well known in the art and generally referred to as "I.V. transmissions". Because the power generating efficiency of most engines or prime movers is highest in only a limited range of operating speeds, I.V. transmissions have and continue to generate much interest as a potentially ideal solution to the transmission of power from a power source to a power consuming load which must be driven at speeds varying from the operating speeds of the power source.
Mechanical I.V. transmissions are generally embodied in a structural organization capable of transmitting torque by friction between two or more traction surfaces on relatively rotatable bodies supported in such a manner as to enable the traction surfaces to be retained against one another under a normal force adequate to prevent slippage between the surfaces. The infinitely variable speed ratio is achieved by designing the torque arm or radius of one of the bodies to be continuously variable relative to the radius of the other body. The geometric configuration of two such bodies capable of attaining this result is exemplified by a wheel shiftable axially on a disc or a ring shiftable along the axis of a cone.
In a commonly assigned co-pending U.S. application Ser. No. 706,291, filed July 19, 1976, by Yves Jean Kemper, now U.S. Pat. No. 4,152,946 issued May 8, 1979, the present inventor, several embodiments of an I.V. transmission are disclosed in which torque is transmitted between a first body, represented by a pair of axially movable internal traction surfaces of revolution about a first axis, and a second body represented by a pair of external cone-like traction surfaces of revolution about a second axis inclined with respect to and intersecting the first axis at a point of axes intersection. The second body is supported rotatably on its own or second axis in a crank-like supporting body journalled for rotation about the first axis. Torque applied to the crank-like body results in nutational movement of the second axis about the first axis and rotation either of the second body about the second axis or of the first body about the first axis. In embodiments where the first body is held against rotation as a reaction member, the second body rotates about the second axis as a result of its frictional engagement with the traction surfaces on the first body at two points of engagement spaced equally and oppositely along the first axis from the point of axes intersection. A pinion gear coupled at one end of the second body orbits in planetary fashion about the first axis while in mesh with an orbiting idler engaged with a sun gear carried on an output shaft. The planet gear output in such a transmission offers flexibility in the transmission design by which a unidirectional constant velocity input may be transmitted as an output varying from zero to the approximate speed of the input in one direction; varying from zero to input velocity but in the opposite direction; or varying continuously from an intermediate output speed in the same direction as the input through zero to a directional reversal of the input.
While the state of the art relating to I.V. transmissions has been developed to a point of practical application in transmitting power of magnitude corresponding to that required by automotive vehicles and higher, the efficiency curve for an I.V. transmission, whether it be of the type disclosed in the afore-mentioned copending application or any of several other types, is the approximate reciprocal of the torque function of the power transmitted. At constant input power, therefore, transmission efficiency is highest with increased output speeds and lowest at low output speeds where torque multiplication is greatest. The need for improvement in an I.V. transmission system by which operating efficiencies can be improved while at the same time retaining the speed varying capabilities thereof will thus be appreciated by those skilled in the art.